1. Field of the Invention
This invention relates to the desalination of water by removal of both negative and positive ions of a salt from an aqueous solution. More specifically, the invention relates to a process for separating ions of a salt from aqueous solution by employing an ion exchange resin in a unique simulated moving bed flow scheme.
2. Background Information
It is known in the separation art that certain ion exchange resins, particularly thermally regenerable resins, can be used in separating components from a fluid mixture, particularly salts from an aqueous solution, i.e., the desalination of water. Examples of such art are U.S. Pat. Nos. 4,293,423 to Kosaka et al, 4,206,051 to Bolto et al, 4,202,737 to Shimizu, 4,184,948 to Dabby et al, 4,087,357 to Barrett et al, 4,039,442 to Kadlec et al, 3,716,481 to Battaerd, 3,351,549 to Bloch, 3,231,492 to Stine et al and 3,133,016 to Stine et al. All of the above references teach adsorption of the ions of the salts at relatively low temperature and desorption of the ions or regeneration of the resin at a higher temperature. Some of the above references, i.e., Kosaka et al and Shimizu, disclose continuous processes wherein the resin is physically moved from one location to another for adsorption and desorption to occur. These references show systems where only a single moving bed column is used with various portions of the column comprising specific zones where particular operations such as adsorption, regeneration or buffering occur.
The principal of the simulated countercurrent moving bed to continuously separate, in liquid phase, an extract component from a mixture with a raffinate component by contact with adsorbents selective for the extract component is also known to the art. The basic teaching of the simulated moving bed countercurrent process flow scheme is in Broughton et al U.S. Pat. No. 2,985,589. In the Broughton et al scheme, three and preferably four zones are required in the adsorbent bed including buffer or purification zones whereby liquid which does not exit the column via the raffinate and extract stream outlets continues through the column and serves to flush the downstream (with reference to the direction of liquid flow) adsorbent prior to its simulated movement into the adsorption and desorption zones, respectively. In the above Bloch patent, it is taught that the flow described in Broughton et al may be applied to water desalination.
I have discovered a new simulated countercurrent moving bed flow scheme particularly applicable to the use of a thermally regenerable ion exchange resin and the desalination of water.